Cellulosic and lignocellulosic feedstocks (e.g., plant-derived biomass) provide a large renewable source of potential starting materials for the production of a variety of chemicals, plastics, fuels and feeds. For example, biomass feedstocks comprise a variety of carbohydrates which can be hydrolyzed to provide fermentable sugars for use in the production of alcohol fuels, such as ethanol, methanol, and butanol.
The use of biomass feedstocks for production of biofuels is motivated by both economic and environmental concerns, including reduction of greenhouse gas emissions, enhancement of the fuel supply, and maintenance of the rural economy. Energy legislation enacted in 2007 in the United States provides that yearly ethanol production reach 136.3 billion liters by the year 2022, with at least 79.5 billion liters coming from lignocellulosic feedstocks, such as corn stover, prairie grass, and poplar trees, as opposed to corn grain, which comprises a high amount of more easily hydrolyzed starch. See, e.g., Ethanol Producer Magazine, December 2007.
For recent reviews concerning biomass-to-ethanol conversion strategies see DiPardo, Journal of Outlook for Biomass Ethanol Production and Demand (EIA Forecasts), 2002; and Lynd, et al., Current Opinion in Biotechnology, 16, 577-583 (2005). The conversion of biomass to ethanol can involve significant amounts of water and energy, particularly in saccharification steps. Due to the complex structure of cellulosic and lignocellulosic materials, some form of chemical, thermal, mechanical, or enzymatic pretreatment is generally needed to increase saccharification of the carbohydrates. See Chen, Y., et al., Appl. Biochem. Biotechnol. 143, 80-92 (2007). Further, raw biomass tends to be bulky, but can lose significant value if exposed to the weather, thus necessitating large weather-proof biomass storage facilities. Still another significant obstacle for converting biomass into ethanol or other biofuels is the cost involved in transporting large volumes of the relatively low density biomass to centralized biofuel production facilities for processing. For a discussion of the costs associated with trucking various biomass materials, see Kumar et al., Bioresource Technology, 96, 819-829 (2005).
Thus, there is a continuing need for improved processes and systems for converting biomass to biofuels and/or high density biofuel feedstocks. In particular, there is a need for efficient processes that can reduce biomass storage and transport issues, and which do not require the use of large amounts of externally provided water.